Perforated tube combustion apparatus and process



p 1964 o. A. DAVIS, 92.. ETAL PERFORATED TUBE COMBUSTION APPARATUS AND PROCESS 2 Sheets-Sheet 1 Filed NOV. 10, 1961 v INVENTORS ORV/.5- ,4. DAV/5, SE.

Sept. 29, 1964 O. A. DAVIS, SR. ETAL PERFORATED TUBE COMBUSTION APPARATUS AND PROCESS Filed Nov. 10 1961 2 Sheets-Sheet 2 m in m m m.

m m n (0 O 0' '3 0) M O O 'a 9 G) O O O 0 (0 O O O 0 i) (0 O O O 0 0 O 0 O '4 :2. (D O O O 0) (0 O O O 0) 0 /60 (0 O O O 0 (0 O O O O (D O O O Q (D O O O o) (D WW "o up INVENTORS 0/1 /45 ,4. D4V/s, s/a MAC/M51 a F/P4/V/10FF 4 TTOE/VE' Y United States Patent C) 3,150,708 PERFORATED TUBE COMBUSTION APPARATUS AND PROCESS Orvis A. Davis, Sr., Allison Park, and Michael G. Frankofi, West Deer Township, Allegheny County, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Filed Nov. 10, 1961, Ser. No. 151,525 14 Claims. (Cl. 158--28) This application is a continuation-in-part of Serial Number 5,712 filed February 1, 1960, now abandoned.

This invention relates to improvements in liquid fuel burner apparatus and to process for the use of said apparatus.

The improved liquid fuel combustion apparatus of this invention comprises in combination a perforated flame holder tube having a longitudinal axis, the opening at one end of the perforated tube adapted to receive an aspirating nozzle and the opening at the other end of the perforated tube adapted for the discharge of flame gases, an aspirating nozzle disposed at the nozzle end of the perforated tube coaxially therewith and a flame spreader baflle disposed near the discharge end of the perforated tube on a plane normal to the axis of the tube, the flame spreader baflle being spaced apart from the discharge end of the perforated tube by an axial distance whereby the unobstructed area between the discharge end of the perforated tube and the flame spreader baflle available for discharge of flame gases from the perforated tube is partially reduced or restricted as compared to the transverse cross sectional area at the discharge end of the perforated tube, the discharge area being obstructed by an amount which improves combustion in the apparatus.

The nozzle positioned coaxially with respect to the perforated tube at one end thereof for spraying liquid fuel within the perforated tube longitudinally to the other end thereof must be an aspirating nozzle. The aspirating nozzle employed has conduit means extending to it from a source of superatmospheric air and has separate conduit means extending to its from a liquid fuel reservoir containing liquid fuel under substantially atmospheric pressure. The nozzle is adapted so that the passage of superatmospheric air through the nozzle aspirates liquid fuel existing under atmospheric pressure through the nozzle and sprays an air-oil mixture into the perforated flame holder tube.

The mixture of fuel and air passing along the length of the perforated tubular flame holder is ignited by means of any suitable igniter disposed within or in the vicinity of the perforated tube and the flame gases pass through the perforated tube from the nozzle end to the discharge end thereof. The diameter of the perforated tube is proportional to the quantity of oil and air in the spray mixture and is sufliciently large to contain the flame passing longitudinally therethrough but sufiiciently small so that the passage of flame gases within the tube creates an aspirational elfect along the tube inner wall causing inflow of atmospheric air through the tube perforations along the axial extent of the tube.

The flame spreader baflle member is disposed near the discharge end of the perforated tube on a plane normal to the longitudinal axis of the tube. The flame spreader is disposed sufliciently close to the perforated tube so that the area of the discharge opening defined between the discharge rim of the perforated tube and the baflle available for discharge of flame gases is advantageously about onehalf or less than the discharge opening area that existed in the absence of the flame spreader baflie. However, the flame spreader baffle is not disposed sufliciently close to the perforated tube to completely obstruct the discharge opening of the tube and thereby force discharge of the flame gases through perforations in the flame tube. In general, the axial distance of the flame spreader baffle from the discharge end of the perforated tube should be between about one-fourth or one-eighth and one-fortieth the diameter of the perforated tube at its discharge end and preferably between about one-tenth and one-thirtieth.

In order to effect a reduction of the discharge opening of a cylindrical perforated tube having a radius r by disposing a flat flame spreader baflie of a radius greater than v near the discharge end of the tube on a plane normal to the longitudinal axis of the tube, the bafiie must be disposed at an axial distance which is less than one-half r from the end of the tube. The reason is that in the absence of the baffle member the discharge area at the end of the perforated tube is n-r while, when employing a bafile member as described, the available discharge area for flame gases defines a cylinder and is 21rrh, where h is the axial distance of the baffle plate from the discharge end of the perforated tube. It is therefore seen that in order for the discharge area for the flame gases, when employing the flame spreader baflle, to be equal to or less than the discharge area in its absence it is necessary that h be onehalf of r or less and in order for the discharge area to be one-half or less than the discharge area in its absence it is necessary that h be one-fourth of r or less.

When employing the apparatus of the present invention for the combustion of liquid fuel oil it is essential that the nozzle employed be of the aspirating type wherein oil under atmospheric pressure is drawn into the nozzle by aspiration. The apparatus of the present invention is not operative for the combustion of liquid fuel when employing a nozzle to which oil is supplied under pressure. There is a two-fold reason why the apparatus of the invention must utilize an aspirating nozzle rather than a pressure type nozzle when spraying liquid fuel. First, the spray from the aspirating nozzle is a mixture of liquid fuel droplets suspended in air and it has been found that a mixture of liquid fuel droplets in air from an aspirating nozzle is capable, during transit through a perforated tube, of inducing a significant vacuum along the interior wall of the tube throughout the axial extent thereof so that substantial inflow of atmospheric air through the tube perforations results. This inflow of atmospheric air through the tube perforations yields the two-fold advantage of providing secondary air required for combustion and keeping oil droplets away from the tube wall and in the flame proper so that they can be burned rather than wet the walls of the tube and drain therefrom. On the other hand, the use of a pressure type nozzle produces a spray of oil droplets which upon combustion within a perforated tube is not able to induce a measurable vacuum along the inside wall of any perforated tube no matter what its diameter. For this reason inward aspiration of atmospheric air through the perforations of a perforated tubular flame holder used in conjunction with a non-aspirating pressure-type fuel oil nozzle is not possible.

The second and most important reason for employing an aspirating nozzle in the apparatus of this invention is that the oil droplets contained in the spray from an aspirating nozzle are of a size considerably smaller than the size of the oil droplets that can be obtained from a presure type nozzle spraying the same quality of liquid fuel at the same rate. For example, it has been found that atomization of liquid oil with an aspirating nozzle produces a spray containing many times the number of oil particles as can be obtained in the spray from a pressure type nozzle through which the same oil is sprayed at the same rate. Therefore, the size of the oil particles from the aspirating nozzle are necessarily much smaller than the size of the oil particles from a pressure type nozzle.

When an aspirating nozzle is disposed at one end of a perforated tube coaxially therewith and sprays a liquid fuel and air mixture along the length of the perforated tube and the mixture is ignited, a flame of light yellow coloration is discharged from the opposite end of the perforated tube. The movement of a baffle disposed on a plane normal to the longitudinal axis of the tube from a distant point into the end of the flame discharging from the perforated tube at first produces no apparent effect upon combustion.characteristics. However, as the baffle member moves sufficiently close to the discharge end of the perforated tube so that the area between the rim of the perforated tube and the portion of the baffle closest thereto available for discharge of the flame gases becomes restricted as compared to the cross sectional area of the perforated tube, andpreferably becomes restricted to the extent of being one-half or less than the cross sectional area of the discharge end of the, perforated tube, a surprising and unexpected change in flame characteristics occurs. At approximately this distance from the discharge end of the perforated tube the flame spreader baflle induces a change in color of the flame in the region between the baflle and the discharge end of the perforated tube. In this region the yellow coloration of the flame disappears and is replaced by a light blue hue indicating a change from partial to complete combustion in this region.

The inducement of the blue flame coloration is highly surprising in view of the fact that the flame spreader baffle substantially obstructs the opening available for discharge of the flame gases. The axial distance of the flame spreader baffle from the end of the perforated tube which is required to achieve this advantageous result is critical. Moreover, the flame spreader baffle must not be excessively close to the discharge end of the flame holder. If the axial distance of the flame spreader bafl le from the end of the perforated tube is less than about one-fortieth of the diameter of the perforated tube at its discharge end the advantage of the invention is lost and greatly inferior flame characteristics occur. At such small axial distances from the discharge end of the perforated tube the flame discharge passage becomes so severely obstructed that the flame begins to exit from the flame holder tube perforations. When this occurs the light blue hue disappears and a smoky flame having a deep yellow coloration is induced. This flame is highly inferior to even the flame achievable in the absence of a flame spreader baflle.

When the flame spreader baflfe is disposed at an axial distance from the discharge end of the perforated tube as defined for this invention a further highly surprising effect in the apparatus was observed. It has been discovered that when the flame spreader baflle is disposed at an axial distance from the end of the perforated tube equal to between about one-eighth and one-fortieth of the discharge diameter of the tube, an increase in vacuum occurs along the inside wall of the perforated tube near the discharge end thereof and this increase is sufliciently great to be measured. This observed increase in vacuum is highly unexpected since the flame spreaderconstitutes a severe obstruction against the discharge of flame gases and it would ordinarily be predicted that any such obstruction would increase the pressure within the flame holder. Although not bound by any theory it appears that the observed increase in vacuum along the inner wall of the perforated tube, when employing a flame spreader baflle at a distance from the end of the perforated tube in accordance with this invention, occurred as a result of high flame gas velocity along the surface of the flame spreader baflle facing the perforated tube and this high flame gas velocity induced an increase in the vacuum in the discharge end region of the perforated tube which in turn induced higher aspiration rates of atmospheric air thereby contributing increased air supply to the flame and causing more complete combustion. Furthermore, the high temperature of the flame spreader caused by direct flame impingement thereon is likely to have insulated the flame against heat loss in the region at the discharge end of the 4 perforated tube and this effect also probably contributed, to a smaller extent, to the improvement in flame characteristics.

During combustion with the apparatus of this invention, it frequently occurs that the distance of the flame spreader from the discharge end of the perforated tube must be either intermittently or continuously adjusted in order to achieve the advantage of the invention. Even under static operating conditions, very small variation of the distance between the flame tube and the flame spreader within the range of this invention has a great effect upon flame coloration or upon the increase in vacuum along the inner wall of the perforated tube and therefore the precise position for optimum operation is generally not predictable prior to actual combustion. Furthermore, during actual operation conditions do not generally remain static. For example, fluctuations in pressure of aspirating air occur as well as variations in the level in the oil reservoir. These often necessitate provision of means for the adjustment of the distance between the flame spreader and the flame tube during operation. Therefore, the spacing adjustment means employed must be disposed and adapted to permit adjustment to occur during operation. If desired, the spacing can be performed automatically. For example, at an optimum spacing distance the flame temperature between the discharge end of the perforated tube and the flame spreader will be at a maximum and this temperature can serve as a variable for automatic control of the distance between the flame spreader and the flame tube. Also, the vacuum along the inner Wall of the flame tube at the discharge end can be measured and utilized as a control variable. No matter whether continuous or intermittent control is employed, the provision of means for adjustment of the axial distance between the flame spreader and the flame tube provides advantageous combustion control.

In terms of process, this invention comprises aspirating liquid fuel under substantially atmospheric pressure through an aspirating nozzle by means of air under superatmospheric pressure, discharging the air and oil from the nozzle as a spray, igniting said spray to produce a flame, directing said flame longitudinally through a perforated tube having an inlet end and a discharge end, removing flame gases from said discharge end, disposing a baffle near the discharge end but spaced apart therefrom, and adjusting the distance between the discharge end of the perforated tube and the baflle in response to flame temperature, color or some other variable to achieve an improvement in flame characteristics.

Each of the elements in the combination comprising the present invention exists in interdependent relationship with the other elements and the results obtained with the combination as recited are completely impossible of attainment in the absence of any one of the elements. For example, it was found that employing an aspirating nozzle in cooperation with a flame spreader baffle in the absence of a perforated tube produced no advantageous effect upon flame characteristics. In the absence of the perforated tubular flame holder, placing a baflle transversely against an aspirating nozzle burner flame at various points along the length of the flame caused the tip of the flame, upon striking the baffle, to reflect back into the base of the flame thereby surrounding the base of the flame and depriving it of the air necessary for complete combustion. Employment of a baffle in the absence of a perforated tube caused the flame to assume a deeper yellow coloration indicating highly incomplete combustion and also resulted in severe soot deposition upon the baflic. It is therefore seen that the perforated tube is a highly interdependent structural feature in the apparatus combination of this invention in that it not only guarantees aspiration of atmospheric air into the flame but also works cooperatively with the flame spreader baflie so that when the battle is employed as described in this invention not only is the base of the flame not deprived of air but the inward aspiration of atmospheric air through the flame holder perforations is actually increased.

No comparable results could be achieved when employing a pressure type nozzle in combination with a perforated tube and a flame spreader baffle, the use of a flame tube and a flame spreader with a nozzle through which liquid fuel is supplied under pressure producing a highly inferior flame as compared to the flame from the same nozzle in the absence of the flame tube and flame spreader. As previously noted, charging the atomized oil spray from a pressurized nozzle through a perforated tube does not result in any detectable aspiration of atmospheric air through the tube perforations. When a flame spreader baffle on a plane transverse to the longitudinal axis of the perforated tube was moved into the end of the flame from a pressure type liquid fuel nozzle it was observed that instead of the characteristics of the flame improving the reverse occurred. As the flame spreader bafile moved to the vicinity of the discharge end of the perforated tube it was observed that the flame assumed a deeper yellow coloration, became smoky and the batfle member became wet with oil. As already noted the particles of oil in the spray from a pressure nozzle are appreciably larger than the oil particles from an aspirating nozzle. The oil particles in the spray from a pressure type nozzle are evidently sufliciently large so that they do not completely burn or vaporize prior to impinging upon the flame spreader. This was evidenced by the flame spreader instantly becoming wet with oil upon starting operation with a pressure type liquid oil nozzle, a phenomenon that does not occur when employing an aspirating nozzle even with perforated tubes which are much smaller in length. At the end of tests employing a pressure type nozzle the entire assembly, including both the perforated tube and the spreader baflle, were found to be coated with liquid oil and soot. In contrast, when employing an aspirating nozzle, at the end of tests of either short or long duration the entire assembly, including the flame holder and the flame spreader baffle, were observed to be entirely free of liquid oil and soot.

Attention is now directed to the drawings wherein:

FIGURE 1 is a longitudinal cross section of an aspirating nozzle which can be employed in the apparatus of the invention,

FIGURES 2 and 3 are longitudinal and transverse cross sectional views, respectively, of a preferred aspirating nozzle for use in the apparatus of the invention,

FIGURE 4 shows an aspirating nozzle, a partially cutaway perforated flame holder and flame spreader in combination, and

FIGURES 5 and 6 are top views of two different flame spreaders.

FIGURE 1 illustrates the internal structural details of the nozzle 30. The nozzle 30 comprises a tubular body portion 34 having an inturned lip 36 at one end. The other end of the tubular body portion 34 is threaded internally and externally, as shown, with a cap 38 in threaded engagement with the external threads on the body portion 34 so that the cap 33 fixedly secures a mounting ring 33 in a position encircling the body portion 34. Mounting ring 33 receives fastener 32 which extends transversely from the nozzle 30 for securing the nozzle within a flame tube. The cap 38 is provided with an axial opening 42 that passes through an external threaded boss 44. An air supply conduit 46 is connected to the cap 38 by a coupling member 48 whereby air can be introduced to the interior of nozzle body 34 under a moderate pressure, for example, at a pressure of about 2 to pounds per square inch.

A swirl stem 5% is threaded as shown and secured within the nozzle body 34. The portion of the swirl stem 50 adjacent the cap 38 is provided with an axial passageway 52 that communicates with a transverse passageway 54, whereby air from the conduit 46 may pass into the annular space between the nozzle body 34 and the swirl stem 50 through the transverse passageway 54. A pair of orifice plates 56 and 58 are retained against the lip 36 by engagement of a frusto-conical end portion 60 of the swirl stem 50 bearing against a complementary surface of the orifice plate 53. The swirl stem 50 terminates in a shouldered fashion as indicated at 62 and in a reduced truncated conical tip 64. The orifice plate 58 is provided with an axial orifice 66 that communicates with a swirl chamber 68 defined by spacing of the extremity of the swirl stem 50 from the orifice plate 58. The orifice plates 56 and 58 are in sealing engagement about their extremities but these plates are slightly spaced as at 70 for an interval outwardly from their centers. The orifice plate 56 is provided with an axial discharge orifice 72 somewhat larger in diameter than the orifice 65 in the orifice plate 58.

Communication is provided between the space 70 intermediate the orifice plates 56 and 58 and the exterior of the nozzle body 34 by means of a passageway 74 in the orifice plate 58 that communicates with a passageway 76 in the nozzle body 34. An external conduit 78 is secured to the exterior of the body by a means such as brazing 80 or the like, whereby fuel can be introduced from the conduit 73 to the space 70 intermediate the orifice plates 56 and 58.

The frusto-conical portion 60 of the swirl stem 50 is provided with a plurality of circumferentially spaced, inclined slots, one of which is shown at 82, such slots 82 affording fluid communication between the annular space intermediate the swirl stem 50 and the nozzle body 34 and the swirl chamber 68 so that air moving from such annular space into the swirl chamber 68 will have a rotary or swirling motion imparted thereto.

In the operation of the aspirating nozzle shown in FIGURE 1, air is introduced into the nozzle 30 at a moderate pressure of about 2 to about 10 pounds per square inch and, with the nozzle 30 being dimensioned for a fuel flow rate of about 0.1 to 1.0 gallon per hour, the air flow rate is about 7.0 to 70.0 cubic feet per hour. Obviously, such air pumping requirement is very low or minimal and can be met by very simple and inexpensive air pumps such as a conventional rotary vane type. Air entering the nozzle 30 passes through the passageways 52 and 54 into the annular space between the swirl stem 50 and the nozzle body 34, thence enters the swirl chamber 68 with a swirling motion through the slots 82, and thereafter exits from the nozzle through the orifices 66 and 72 in the orifice plates 58 and 56, respectively. Such passage of air through the nozzle 30 results in a subatmospheric pressure in the space 70 between the orifice plates 56 and 58. Such subatrnospheric pressure serves to aspirate or draw liquid fuel such as fuel oil into the space 70 through the passageways 74 and 76 and the conduit 78, it being understood that the conduit 78 is connected to a supply of fuel. The aspiration of fuel into the nozzle 30 proceeds even when the fuel supply is under atmospheric pressure and is disposed at a position lower than the nozzle 30. In fact, it is preferred that the fuel supply be on the order of a few inches below the nozzle 30 when the latter has a capacity such as that outlined above. Fuel entering the space 70 migrates to the region of the orifices 66 and 72 whence the fuel is picked up and discharged along with the air from the nozzle 30 in the form of a fine mist or spray of liquid droplets.

FIGURE 2 is a longitudinal cross sectional view taken through the axis of a preferred aspirating nozzle designated generally as and having a tubular body portion 142 which is internally and externally threaded as shown. The forward end of body portion 142 terminates with a substantially flat integral enclosure 144 which is on a plane transverse to the longitudinal axis of tubular body 142. Enclosure 144 has an orifice opening 146 which is the apex of an axial conical bore 148.

7 A plug 150 having external threads and an axial bore 82 is equipped with two or more prongs 84 on its rear face so that it can be screwed into the interior of tubular body 142 as shown. Plug 150 has a central forwardly projecting stud 86 terminating with a frusto-conical swirl stem 88 which abuts firmly against the complementary interior surface of the base portion of conical bore 148 leaving unoccupied the apex of conical bore 148, said unoccupied apex constituting a swirl chamber 90. Swirl stem 88 has one or more peripheral slots 92 extending the length of the stem and providing passage between air chamber 94 and swirl chamber 90. Axial bore 82 constitutes a connecting passageway into swirl chamber 90 for the suction of liquid fuel oil from an oil reservoir 83 disposed on a level lower than the nozzle. Axial bore 82 protrudes a portion of the distance into swirl chamber 90 by means of cylindrical tube 149.

A cap designated generally as 95 encloses the forward outer portion of tubular body 142 and the end enclosure 144 of tubular body 142. FIGURE 3 is a view facing the cross section taken on plane 33 of FIGURE 2. Cap 95 has a side portion 96, a top portion 98 and an orifice opening 100 in the center of the top portion which opening is larger than orifice opening 146. Cap 95 is screwed in sealing engagement with tubular body 142 and the .top portion 98 is spaced apart from enclosure 144 to form a second swirl chamber 102. A hollow rib 104 which is integral with side 96 of cap 95 has a circular interior chamber 106 from which one or more passageways 108 approach chamber 102. Passageways 108 approach chamber 102 tangentially as shown in FIGURE 3. An inlet passage 110 to chamber 106 is provided through the interior of boss 130.

A cylindrical duct 134 extends from orifice 146 axially into cylindrical orifice 100. Duct 134 can extend a 7 portion of the distance to orifice 100 but preferably extends into orifice 100, as shown. The outer diameter of duct 134 is less than the diameter of orifice 100, providing a diameter differential therebetween. When the duct 134 extends into orifice 100, the diameter of orifice 100 can be smaller than would be otherwise required.

After the plug 150 is screwed tightly into the interior of tubular body 142 and the cap 95 is screwed onto the exterior of tubular body 142, as shown, the resulting nozzle assembly is secured into position for use, for example, by screwing tubular body 142 into an internally threaded circular frame 112. Circular frame 112 has one or more transverse internally threaded receptacles for receiving lateral supporting ties 152. After the nozzle is assembled and secured axially into one-end of an elongated perforated tube, as shown in FIGURE 4, oil reservoir 83, which is open to the atmosphere, is connected to the nozzle at externally threaded boss 114 extending rearwardly from the center of plug 150 and coaxial with oil passageway'82. Suitable flared tubing 116 is attached in sealing connection to boss 114 by means of nut 118. Aspirating air flows to chamber 94 from pressurized chamber 127 through valve 125 and passageway 120 in plug 150 terminating with rearwardly extending externally threaded boss 122 to which flared tubing 124 is attached in sealing connection by means of internally threaded nut 126'. The aspirating air is under a slightly superatmospheric pressure such as, for example, 3 pounds per square inch :gauge. Superatmospheric air is also supplied to chamber 106 through passageway 110 from pressurized chamber 127 by attaching flared tubing 128 in sealing connection with boss 130 by means of nut 132. Tube 128 and 1 24 are tied intoeach other by means of connecting tube 136 having a valve 138.

In operating the nozzle shown in FIGURES 2 and 3 to aspirate the oil in reservoir 83, slightly superatmospheric air is charged through air passageway 120 to air chamber 94 from which it is passed through slots 92 and approaches swirl chamber 90 in a substantially tangential manner.

The air swirls in swirl chamber creating an evacuated axial vortex which draws fuel oil from reservoir 83 through tube 116, axial passageway 82 and duct 149 into swirl chamber 90 to form a first mixture of air and oil. Duct 149 allows the air to assume an adequate swirling and axial pattern of movement prior to exposure of oil to it. The cylindrical configuration of the outer surface of duct 149 prevents transverse motion of air across its open end, thereby preventing air back pressure against oil from the reservoir. In the absence of duct 149 substantially no aspiration of oil from the reservoir would occur. The mixture passes through orifice opening 146 and duct 134 into second orifice 100. Additional pressurized air enters swirl chamber 102 through tube 128, having open valve 138, bore 110, annulus 106 and tangential slot 108. The additional air swirls in chamber 102 and is then emitted through orifice where it draws into itself the air-oil mixture passing through duct 134 to form a new air-oil mixture which is richer in air. Operation of the nozzle can be terminated merely by closure of air valves and 138 without ensuing drippage of oil from the nozzle by virtue of the oil reservoir 83 being disposed below nozzle level.

FIGURE 4 shows a complete combination apparatus of this invention including a partially cutaway perforated flame holder 160 having a plurality of perforations 162 along its axial extent to the discharge end thereof. Aspirating nozzle 140 is disposed fixedly in an axial position at one end of perforated flame holder 160. Aspirating nozzle 140 is secured within circular frame 112 and a complementary circular frame 164 is attached to the inner surface of the flame holder. A plurality of lateral ties 152 extend between the complementary circular frames 112 and 164 for securing aspirating nozzle 140 into position. Although circular frame 164 secured Within perforated tube is shown as exposing most of the nozzle end opening of the perforated tube to the atmosphere, circular frame 164 can alternately be constructed in the form of a circular plate having a relatively small central opening for receiving the aspirating nozzle whereby most of the nozzle end of the perforated tube is enclosed. In such a construction the circular plate can be provided with an opening of adjustable size for varying the quantity of air introduced through the nozzle end of the flame holder 160.

Aspirating nozzle 140 is supplied with superatmospheric air from an air compressor 127 and is supplied with liquid fuel from a reservoir 83 which is open to the atmosphere and which is on a level about a few inches below that of the nozzle. Perforated tube 160 is preferably cylindrical in shape as shown but can vary somewhat from a cylindrical configuration. Variations from cylindrical tube configurations include tubes whose walls are slightly uniformly divergent or convergent with increasing distance from the aspirating nozzle. The diameter of perforated tube 160 is proportioned to the quantity of air and oil being sprayed from aspirating nozzle 140 and the diameter is sufficiently large to contain the flame produced upon combustion of the nozzle spray and sufliciently small so that flame gases pass close to the inner wall of the perforated tube and aspirate atmospheric air through the perforations 162. The length of perforated tube 160 can advantageously be longer than the length of the flame from the aspirating nozzle produced in the absence of a perforated tube. The reason is that inflow of air through perforations 162 provides secondary air required for complete combustion of the spray from the nozzle and as long as there is unburned material in the spray inflow of air through perforations 162 will support further combustion. The perforated tube can serve to support combustion until completion thereof and this can be accomplished by providing a perforated tube of length sufficient that a flame is maintained until no more combustible material remains. In experiments it has been found that the length of the flame from 9 an aspirating nozzle can be increased considerably by utilizing a perforated tube whose length is considerably greater than the flame length existing in the absence of a perforated tube.

At the discharge end of perforated tube 160 disposed on a plane transverse to the longitudinal tube axis is a flat circular flame spreader 166 having a diameter greater than the diameter of the perforated tube. Although the top and bottom surfaces of flame spreader 166 are both flat it is especially noted that the surface facing the perforated tube is flat and lies on a plane normal to the axis of the perforated tube. The flame spreader 166 is preferably circular in configuration but can have another configuration, for example, a rectangular configuration. Flame spreader 166 is secured a critical axial distance from the discharge end of perforated tube 160 by means of spacing bolt 174. The axial distance between perforated tube 160 and flame spreader 166 is advantageously ad'- justable. The adjustable spacing means shown in FIG- URE 4 utilizes two brackets 168 and 176, each attached to the outer periphery of the flame tube near its discharge end. Bracket 168 has an opening therethrough in vertical register with a corresponding opening extending through boss 180 in flame spreader 166. Boss 180 is utilized to impart rigidity to the structure and the opening therethrough contains threads to engaged the threads in bolt 174. The unthreaded portion of bolt 174 extends through and is rotatably locked within the opening in bracket 168 while the threaded portion of bolt 174 extends through the opening in boss 180 in threaded engagement therewith. The head of bolt 174 is nearer to the flame tube than the flame spreader so that it will be away from the flame and will be cooled by air being drawn into the flame tube. This arrangement permits spacing adjustment during operation of the burner. Spacing adjustment must frequently be made during operation of the burner in response to observed changes in flame characteristics. Dowel 178 depends from the bottom of flame spreader 166, to which it is attached, and extends into a corresponding opening which is larger than itself in bracket 176 so that, upon rotation of bolt 174, the engagement of dowel 178 with bracket 176 prevents rotational movement of flame spreader 166 but permits axial movement thereof. The range of axial adjustment between the flame spreader 166 and the discharge end of flame tube 160 is critical and is preferably between about one-fourth and one-fortieth of the diameter of the perforated tube.

FIGURE 5 shows a top view of the flame spreader plate 166 of FIGURE 4. FIGURE 6 shows an alternate flame spreader 170 containing a plurality of perforations 172 near its center. When flame spreader 170 is disposed a critical axial distance from the discharge end of perforated tube 160 a small amount of the flame will escape through perforations 172 and the flame exiting through these perforations will advantageously possess a blue coloration. The perforations 172 do not add suflicient additional flame gas discharge area to increase the available discharge area for the flame gases to more than the discharge area available for the flame gases in the absence of a perforated tube.

A test was conducted to illustrate the advantage of this invention. In this test an aspirating nozzle similar to the one shown in FIGURE 2 was employed to aspirate .52 gallon per hour of Number 2 fuel oil through the nozzle by means of aspirating air at a pressure of 6 pounds per square inch gauge. The nozzle was placed coaxially at one end of a perforated tube 2 /2 inches in diameter and 6 inches long having circular perforations inches in diameter along its axial extent. The spray within the perforated tube was ignited and a flame spreader baffle was disposed at various distances from the end of the perforated tube. The vacuum along the inside wall of the perforated tube near the discharge end thereof was measured after each adjustment of baffle distance. In order to produce enhanced vacuum measurements at the exposed perforations near the discharge end of the tube, the perforated tube was covered by a metal shield along the two-thirds of its axial extent closest to the nozzle. The results of the test are shown in the following table.

Vacuum Along Flame Axial Distance of Area Available Inner Wall of Coloration in Flame Spreader from for Discharge of Perforated the Region Discharge End of Flame Gases Tube Near the Between the Perforated Tube (Square Inches) Discharge End Flame Spreader (Inches) (Inches of and the Pet- Water) foratcd Tube 4. 9 05 Yellow.* 2.4 .05 Yellow. 2. 0 .06 Yellow. 1.0 .06 Blue. 0. 8 065 Yellow. 0. 5 05 Yellow.

*Flarne coloration at the discharge end of the perforated tube.

As shown in the above table the vacuum along the inside wall of a perforated tube is increased when the flame spreader baflie is disposed at a critical axial distance from the end of the tube. The table indicates also that at a critical axial distance a blue flame coloration replaces the normal yellow flame color, indicating more complete combustion. It is seen from the table that the improvement in vacuum along the inside wall of the perforated tube and the improvement in flame coloration are both sensitive to very slight changes in the axial distance between the flame spreader and the perforated tube.

Various changes and modifications can be made without departing from the spirit of the invention or the scope thereof as defined in the following claims.

We claim:

1. Combustion apparatus comprising perforated tubular flame holder means having a longitudinal axis, liquid fuel oil aspirating nozzle means coaxially positioned at one end of the flame holder means, the other end of the flame holder means comprising a discharge opening means, said flame holder means having perforations along its axial extent to the discharge end thereof, said nozzle means adapted for spraying liquid fuel within the holder means toward said discharge opening means, and flame spreader baffle means near said discharge opening means, the surface of said bafiie means facing said discharge opening means being flat and lying on a plane normal to said longitudinal axis and spaced apart from said discharge opening means, the axial distance between said bame means and said discharge opening means being sufficiently small to partially close said discharge opening means by an amount which induces a vacuum effect at the perforations near the discharge end of said flame holder means.

2. Combustion apparatus comprising perforated tubular flame holder means having a longitudinal axis, liquid fuel oil aspirating nozzle means coaxially positioned at one end of the flame holder means, the other end of the flame holder means having discharge opening means providing an area of discharge, said flame holder means having perforations along its axial extent to the discharge end thereof, said nozzle means adapted for spraying liquid fuel within the holder toward said discharge opening means, flame spreader bafiie means near said discharge opening means, the surface of said baflle means facing said discharge opening means being flat and lying on a plane normal to said longitudinal axis and spaced apart from said discharge opening means, and means for the adjustment of the axial distance between said baffle means and said discharge opening means to partially close said discharge opening means by an amount which induces a vacuum effect at the perforations near the discharge end of said flame holder means.

3. Burner apparatus comprising perforated tubular flame holder means having a longitudinal axis and having nozzle opening means at one end and discharge opening means at the other end, said flame holder means having perforations extending along its axial extent to the discharge end thereof, aspirating liquid fuel oil nozzle means coaxially positioned at said nozzle opening for spraying liquid fuel within the holder means toward the discharge opening means, and flame spreader baffle means disposed near the discharge opening of the flame holder means, the surface of said baflie means facing said discharge opening means being flat and lying on a plane normal to said longitudinal axis, the flame spreader baffle means being disposed sufliciently close to the discharge opening of the holder means that the area'for discharge of flame gases from the discharge opening means of the holder means is reduced by an amount which induces a vacuum effect at the perforations near the discharge end of said flame holder means.

4. Burner apparatus comprising perforated tubular flame holder means having a longitudinal axis and having nozzle opening means at one end and discharge opening means at the other end, said flame holder means having perforations extending along its axial extent to the discharge end thereof, aspirating liquid fuel oil nozzle means coaxially positioned at said nozzle opening means for spraying liquid fuel within the holder means toward the discharge opening means, and flame spreader baflle means disposed near the discharge opening means of the flame holder means, the surface of said baflie means facing said discharge opening means being disposed sufficiently close to the discharge opening means of the holder means that the area for discharge of flame gases from the discharge opening means of the holder means is reduced, and means for the adjustment of the distance between said baflie means and said discharge opening means to restrict said discharge opening means by an amount which induces a vacuum effect at the perforations near the discharge end of said flame holder means.

5. Burner apparatus comprising perforated flame holder means having a longitudinal axis, said flame holder means having nozzle opening means at one end and discharge opening means at the opposite end, said flame holder means having perforations extending along its axial extent to the discharge end thereof, liquid fuel oil aspirating nozzle means disposed at the nozzle opening means of the perforated flame holder means coaxially therewith for spraying liquid fuel to the discharge opening thereof, flame spreader baflle means, the surface of said baflie means facing said discharge opening means being flat and lying on a plane normal to said longitudinal axis and disposed near the discharge opening means of the perforated flame hold-er means, the axial distance of said flame spreader baffle means from the discharge opening of the perforated tube means being between onefortieth and one-fourth of the diameter of the perforated tube discharge opening means and inducing a vacuum effect at the perforations near the discharge end of said flame holder means.

6. Burner apparatus comprising perforated flame holder means having a longitudinal axis, said flame holder means having nozzle opening means at one end and discharge opening means at the opposite end, said flame holder means having perforations extending along its axial extent to the discharge end thereof, liquid fuel oil aspirating nozzle means disposed at the nozzle opening means of the perforated tube means coaxially therewith for spraying liquid fuel to the discharge opening thereof, flame spreader baffle means, the surface of said baffle means facing said discharge opening means being flat and lying on a plane normal to said longitudinal axis and disposed near the discharge opening means of the perforated tube flame holder means, and means for the adjustment of the axial distance between the baffle means and the discharge opening mean of the perforated fl holder means within a range to induce a vacuum effect at 12 the perforations near the discharge end of said flame holder means and equal to between one-fortieth and onefourth of the diameter at said discharge opening means.

7. Burner apparatus comprising perforated tubular flame holder means having a longitudinal axis and having perforations along its axial extent, said flame holder means having nozzle opening means at one end and discharge opening means at the opposite end, said flame holder means having perforations extending along its axial extent to the discharge end thereof, liquid fuel oil aspirating nozzle means, said aspirating nozzle means positioned coaxially with respect to said perforated tube means at the nozzle opening means thereof for spraying liquid fuel within the perforated tube to the discharge opening means thereof, said nozzle means adapted so that passage of pressurized air through said nozzle means aspirates liquid fuel oil under substantially atmospheric pressure through the nozzle means into said perforated tubular flame holder means, said perforated tube means adapted for inflow of atmospheric air through tubular perforations upon combustion with said burner apparatus, flame spreader baffle means disposed near said discharge opening means of the perforated flame holder means, the surface of said baffle means facing said discharge opening being flat and lying on a plane normal to said longitudinal axis, the axial distance of the flame spreader baflle means from the discharge opening means of the flame holder means being adapted to induce a vacuum effect at the perforations near the discharge end of said flame holder means and being between one-fortieth and one-fourth of the diameter of the flame holder means at the discharge opening means.

8. Burner apparatus comprising perforated tubular flame holder means having a longitudinal axis and perforations along its axial extent andliquid fuel oil aspirating fuel nozzle means, said flame holder means having nozzle opening means at one end and discharge opening means at the other end, said flame holder means having perforations extending along it axial extent to the discharge end thereof, said aspirating nozzle means positioned coaxially with respect to said perforated tube means at said nozzle opening means for spraying liquid fuel oil within the perforated tube means to the other end thereof, fuel supply conduit means extending to said nozzle from a fuel oil reservoir means, liquid fuel oil under substantially atmospheric pressure within said fuel reservoir means, air supply conduit means extending to said nozzle means from a pressurized air reservoir means, pressurized air within said pressurized air reservoir, said nozzle means adapted so that the passage of said air through said nozzle means aspirates said liquid fuel through the nozzle means into said perforated tube flame holder means, said perforated flame holder means adapted for inflow of atmospheric air through tube perforations upon combustion with said burner apparatus, flame spreader baflle means, the surface of said batfle means facing said discharge opening being flat and lying on a plane normal to said longitudinal axis of the tubular flame holder means at the discharge opening means of the flame holder means, the axial distance of said baffle means from the discharge opening means of the flame holder means being adapted to induce a vacuum effect at the perforations near the discharge end of said flame holder means and being between one-fortieth and one-fourth of the diameter of the discharge opening of flame holder means.

9. A process comprising aspirating liquid fuel oil under substantially atmospheric pressure through an aspirating nozzle by air under superatmospheric pressure, discharging the air and oil from the nozzle as a spray, igniting said spray to produce a flame, directing said flame longitudinally through an open ended tube having perforations extending along its axial extent to the discharge end thereof to aspirate air through said perforations, discharging flame gases from the discharge end, disposing a baflle whose surface facing said discharge end is flat and 1% lies on a plane normal to the tube axis near the discharge end but spaced apart therefrom, and adjusting the distance between the discharge end of the perforated tube and the baflie to restrict said discharge end and induce a vacuum effect near the discharge end of said perforated tube at the perforations.

10. A process comprising aspirating liquid fuel oil under substantially atmospheric pressure through an aspirating nozzle by air under superatmospheric pressure, discharging the air and oil from the nozzle as a spra, igniting said spray to produce a flame, directing said flame longitudinally through an open ended tube having perforations extending along its axial extent to the discharge end thereof to aspirate air through said perforations, discharging flame gases from the discharge end, disposing a baffle whose surface facing said discharge end is flat and lies on a plane normal to the tube axis near the discharge end but spaced apart therefrom, and adjusting the distance between the discharge end of the perforated tube and the baffle within a range whereby the area of discharge from said flame holder is partially reduced by an amount which induces a vacuum effect near the discharge end of said perforated tube at the perforations.

11. A process comprising aspirating liquid fuel oil under substantially atmospheric pressure through an aspirating nozzle by air under superatmospheric pressure, discharging the air and oil from the nozzle as a spray, igniting said spray to produce a flame directing said flame longitudinally through an open ended tube having perforations extending along its axial extent to the discharge end thereof to aspirate air through said perforations, discharging flame gases from the discharge end, disposing a baffle whose surface facing said discharge end is flat and lies on a plane normal to the tube axis near the discharge end but spaced apart therefrom, and adjusting the axial distance between the discharge end of the perforated tube and the baffle to induce a vacuum effect near the discharge end of said perforated tube at the perforations, the range of adjustment being between one-twentieth and one-fourth of the diameter of the flame holder at the discharge end.

12. A process comprising aspirating liquid fuel oil under substantially atmospheric pressure through an aspirating nozzle by air under superatmospheric pressure, discharging the air and oil from the nozzle as a spray, igniting said spray to produce a flame, directing said flame longitudinally through an open ended tube having perforations extending along its axial extent to the discharge end thereof to aspirate air through said perforations, discharging flame gases from the discharge end, disposing a baflie whose surface facing said discharge end is flat and lies on a plane normal to the tube axis near the discharge end but spaced apart therefrom, and adjusting the distance between the discharge end of the perforated tube and the baflie to obtain a desired change in flame coloration by restricting said discharge end and inducing a vacuum efiect near the discharge end of said perforated tube at the perforations.

13. A process comprising aspirating liquid fuel oil under substantially atmospheric pressure through an aspirating nozzle by air under superatmospheric pressure, discharging the air and oil from the nOZZle as a spray, igniting said spray to produce a flame, directing said flame longitudinally through an open ended tube having perforations extending along its axial extent to the discharge end thereof to aspirate air through said perforations, discharging flame gases from the discharge end, disposing a baffle Whose surface facing said discharge end is flat and lies on a plane normal to the tube axis near the discharge end but spaced apart therefrom, and adjusting the distance between the discharge end of the perforated tube and the baffle to obtain a desired change in flame temperature by restricting said discharge end and inducing a vacuum effect near the discharge end of said perforated tube at the perforations.

14. A process comprising aspirating liquid fuel oil under substantially atmospheric pressure through an aspirating nozzle by air under superatmospheric pressure, discharging the air and oil from the nozzle as a spray, igniting said spray to produce a flame, directing said flame longitudinally through an open ended tube having perforations extending along its axial extent to the discharge end thereof to create a vacuum near said perforations, discharging flame gases from the discharge end, disposing a baffle whose surface facing said discharge end is flat and lies on a plane normal to the tube axis near the discharge end but spaced apart therefrom, and adjusting the distance between the discharge end of the perforated tube and the baffle to obtain a desired change in the vacuum near the perforations in the perforated tube by inducing a vacuum effect near the discharge end of said perforated tube at the perforations.

References Cited in the file of this patent UNITED STATES PATENTS 1,099,613 Oliver et al. June 9, 1914 1,450,229 Robinson Apr. 3, 1923 1,496,180 Smith et a1. June 3, 1924 1,695,334 Johnston Dec. 18, 1928 2,124,328 Yoshinaka July 19, 1938 2,180,190 Baro Nov. 14, 1939 2,669,297 Sherman Feb. 16, 1954 2,948,478 Walsh Aug. 9, 1960 2,984,420 Hession May 16, 1961 

1. COMBUSTION APPARATUS COMPRISING PERFORATED TUBULAR FLAME HOLDER MEANS HAVING A LONGITUDINAL AXIS, LIQUID FUEL OIL ASPIRATING NOZZLE MEANS COAXIALLY POSITIONED AT ONE END OF THE FLAME HOLDER MEANS, THE OTHER END OF THE FLAME HOLDER MEANS COMPRISING A DISCHARGE OPENING MEANS, SAID FLAME HOLDER MEANS HAVING PERFORATIONS ALONG ITS AXIAL EXTENT TO THE DISCHARGE END THEREOF, SAID NOZZLE MEANS ADAPTED FOR SPRAYING LIQUID FUEL WITHIN THE HOLDER MEANS TOWARD SAID DISCHARGE OPENING MEANS, AND FLAME SPREADER BAFFLE MEANS NEAR SAID DISCHARGE OPENING MEANS, THE SURFACE OF SAID BAFFLE MEANS FACING SAID DISCHARGE OPENING MEANS BEING FLAT AND LYING ON A PLANE NORMAL TO SAID LONGITUDINAL AXIS AND SPACED APART FROM SAID DISCHARGE OPENING MEANS, THE AXIAL DISTANCE BETWEEN SAID BAFFLE MEANS AND SAID DISCHARGE OPENING MEANS BEING SUFFICIENTLY SMALL TO PARTIALLY CLOSE SAID DISCHARGE OPENING MEANS BY AN AMOUNT WHICH INDUCES A VACUUM EFFECT AT THE PERFORATIONS NEAR THE DISCHARGE END OF SAID FLAME HOLDER MEANS. 